Dr Galpin begins by breaking down “the week of endurance” by explaining that “you need to do something once a week that gets you to a maximum heart rate, or as high as you can possibly get”.

To work out your max heart rate, he suggests starting with an equation of 220 minus your age. “If you’re 40 years old, your maximum heart rate is probably about 180 beats per minute. Now I can tell you flat out right now, my max heart rate is close to 210, which means I’m 10 years old, so take that number with a grain of salt. That calculation is not a good proxy for physical fitness but it’s a rough number,” he says.

“Another easy way to do it if you have a heart rate monitor is to do the hardest workout you can possibly do, see what the highest number you get is and assume that’s close to your max.”

Don’t have a heart rate monitor? You can always work with something called RPE, which stands for ‘rating of perceived exertion’. This works on an effort scale of 1-10, with 10 being your all-out maximum effort – try to aim for that level of work during this session.

Cardio workouts: the two types of HIIT you need to do every week, according to an exercise professor